Field of the Invention
The invention relates to a method of manufacturing a root pivot assembly of blades of a turbo-machine and more particularly variable incidence stator blades of compressors for aircraft turbo-jet engines.
Background of the Prior Art
The facility of variable orientation of stator blades of the various stages of a compressor is particularly necessary if it is desired to achieve for each stage of the compressor the highest possible pressure rise at a given rating while at the same time maintaining a sufficient margin in relation to the surge region of operation. In order to enable such orientation, the blades generally comprise a tip pivot assembly cooperating with a fixed bearing in the engine casing and actuated by a control device for orientation of the blades, while the blade roots comprise a cylindrical seating which enables them to turn within a bearing disposed within an inner location point of an internal ring of the engine.
Such variable incidnece blades comprising a cylindrical root pivot rotatable within a bearing are described in particular in U.S. Pat. No. 3,990,810, in French patent specification No. 1,114,241 and in French patent application No. 83.19538 filed Dec. 7, 1983 in the name of the present applicant and published under number FR No. 2,556,410 and corresponding to U.S. Pat. No. 4,604,030, issued Aug. 5, 1986.
The manufacture of such blades requires special care since the latter being produced by casting, the mould therefor is complex to produce. On the other hand, the cylindrical seating of the root of the blade must be turned to ensure correct machining of the blade root, which constitutes a supplementary problem, both from the viewpoint of complexity as well as the time required for manufacture and the cost.
The method according to the invention has as its object to simplify the manufacture of a stator blade assembly and in particular the root of the blade with a view to reducing the cost.
A further object of the present invention is to avoid conventional machining operations of the root assemblies of blades with adjustable incidence while at the same time maintaining their facility of turning by means of a pin or peg in a locating recess of the internal ring of the engine.
A further object of the present invention is to simplify the mounting of variable incidence stator blades within the inner ring, and in particular to facilitate the adjustment in height of the blades in a receiving recess of the inner ring, while at the same time minimising the clearances resulting from machining defects or assembly defects.